linux-kernel - Re: [PATCH v2 06/10] cachefiles, erofs: Fix NULL deref in when cachefiles is not doing ondemand-mode

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Date: Tue, 23 Jan 2024 09:32:56 +0800
From: Jingbo Xu <jefflexu@...ux.alibaba.com>
To: David Howells <dhowells@...hat.com>,
 Christian Brauner <christian@...uner.io>
Cc: Jeff Layton <jlayton@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 netfs@...ts.linux.dev, linux-afs@...ts.infradead.org,
 linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org,
 ceph-devel@...r.kernel.org, v9fs@...ts.linux.dev,
 linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Marc Dionne <marc.dionne@...istor.com>, Gao Xiang <xiang@...nel.org>,
 Chao Yu <chao@...nel.org>, Yue Hu <huyue2@...lpad.com>
Subject: Re: [PATCH v2 06/10] cachefiles, erofs: Fix NULL deref in when
 cachefiles is not doing ondemand-mode



On 1/23/24 6:32 AM, David Howells wrote:
> cachefiles_ondemand_init_object() as called from cachefiles_open_file() and
> cachefiles_create_tmpfile() does not check if object->ondemand is set
> before dereferencing it, leading to an oops something like:
> 
> 	RIP: 0010:cachefiles_ondemand_init_object+0x9/0x41
> 	...
> 	Call Trace:
> 	 <TASK>
> 	 cachefiles_open_file+0xc9/0x187
> 	 cachefiles_lookup_cookie+0x122/0x2be
> 	 fscache_cookie_state_machine+0xbe/0x32b
> 	 fscache_cookie_worker+0x1f/0x2d
> 	 process_one_work+0x136/0x208
> 	 process_scheduled_works+0x3a/0x41
> 	 worker_thread+0x1a2/0x1f6
> 	 kthread+0xca/0xd2
> 	 ret_from_fork+0x21/0x33
> 
> Fix this by making cachefiles_ondemand_init_object() return immediately if
> cachefiles->ondemand is NULL.
> 
> Fixes: 3c5ecfe16e76 ("cachefiles: extract ondemand info field from cachefiles_object")
> Reported-by: Marc Dionne <marc.dionne@...istor.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Gao Xiang <xiang@...nel.org>
> cc: Chao Yu <chao@...nel.org>
> cc: Yue Hu <huyue2@...lpad.com>
> cc: Jeffle Xu <jefflexu@...ux.alibaba.com>
> cc: linux-erofs@...ts.ozlabs.org
> cc: netfs@...ts.linux.dev
> cc: linux-fsdevel@...r.kernel.org
> ---
> 
> Notes:
>     Changes
>     =======
>     ver #2)
>      - Move check of object->ondemand into cachefiles_ondemand_init_object()
> 
>  fs/cachefiles/ondemand.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
> index 5fd74ec60bef..4ba42f1fa3b4 100644
> --- a/fs/cachefiles/ondemand.c
> +++ b/fs/cachefiles/ondemand.c
> @@ -539,6 +539,9 @@ int cachefiles_ondemand_init_object(struct cachefiles_object *object)
>  	struct fscache_volume *volume = object->volume->vcookie;
>  	size_t volume_key_size, cookie_key_size, data_len;
>  
> +	if (!object->ondemand)
> +		return 0;
> +
>  	/*
>  	 * CacheFiles will firstly check the cache file under the root cache
>  	 * directory. If the coherency check failed, it will fallback to


Reviewed-by: Jingbo Xu <jefflexu@...ux.alibaba.com>

-- 
Thanks,
Jingbo